Why do people near data centres hear a constant hum, and how loud can it be?
Mostly cooling. Data centres run cooling machinery night and day, and in Chandler, Arizona, residents traced a high-pitched hum to one centre’s air conditioning. US limits are local. Fairfax County, Virginia, allows 60 dBA of steady noise in residential areas by day and 55 at night; since 2024 a new data centre must show, with a noise study at full cooling load, that it complies. Chandler requires new ones to be no louder than the area’s measured background. Both set daytime hours for routine tests of backup generators.
The bigger pictureNear a cluster of Amazon data centres in Prince William County, Virginia, measurements found the noise below the county’s 60-decibel daytime limit about half the time. Residents still said the constant drone, especially at night, cost them sleep. Amazon was muffling its cooling equipment, the local paper reported.
What nobody knows yet
- Nobody publishes a count of how many people live within earshot of a data centre.
- Hum hasn’t found a published follow-up on whether Amazon’s new fans and shrouds quietened Great Oak.
- Rules keep changing: in 2023 Prince William County still exempted air-conditioning noise, and was weighing whether to change that.
Sources (15)
- Prince William Times (Piedmont Journalism Foundation), 27 February 2023 (archived copy) News report
“the city passed an ordinance aimed at bitcoin shops, data centers and marijuana growers, all of which run cooling machinery night and day”
Quote checked on the page, 25 Oct 2026 - Prince William Times (Piedmont Journalism Foundation), 27 February 2023 (archived copy) News report
“Data center noise is unique in that it is not so much its loudness that is an irritant as its constancy.”
Quote checked on the page, 25 Oct 2026 - Prince William Times (Piedmont Journalism Foundation), 27 February 2023 (archived copy) News report
“Measurements taken since last summer at Great Oak, a subdivision south of Manassas plagued by noise from a cluster of Amazon centers, showed that about half the time the noise was below the county daytime limit of 60 decibels.”
Quote checked on the page, 25 Oct 2026 - Prince William Times (Piedmont Journalism Foundation), 27 February 2023 (archived copy) News report
“But residents say the constant drone, especially at night, causes anxiety and deprives them of sleep.”
Quote checked on the page, 25 Oct 2026 - Prince William Times (Piedmont Journalism Foundation), 27 February 2023 (archived copy) Company says so
“Amazon has been working to muffle its cooling equipment with acoustic shrouds and plans to replace all its rooftop fans by September.”
Quote checked on the page, 25 Oct 2026 - Prince William Times (Piedmont Journalism Foundation), 27 February 2023 (archived copy) News report
“People say noise of 55 to 65 decibels (the range of Prince William's noise ordinance limit) is no louder than human conversation, he said, "but it's like having a conversation with someone you don't want to have, all the time.”
Quote checked on the page, 25 Oct 2026 - Prince William Times (Piedmont Journalism Foundation), 27 February 2023 (archived copy) News report
“It exempts noise from air conditioning, but the county may change that.”
Quote checked on the page, 25 Oct 2026 - ABC15 Arizona, on a data centre in Chandler, Arizona News report
“After residents banded together over a high-pitched humming noise, a Chandler data center is promising to fix it.”
Quote checked on the page, 25 Oct 2026 - ABC15 Arizona, on a data centre in Chandler, Arizona News report
“more than 300 signed a petition asking for the city to work with the company to eliminate the noise coming from its air conditioning systems.”
Quote checked on the page, 25 Oct 2026 - Fairfax County, Virginia, Noise Ordinance applicability chart, maximum continuous sound levels in dBA Rule or law
“Residential Areas (as defined herein) in Residential Districts 7 a.m. to 10 p.m. 60”
Quote checked on the page, 25 Oct 2026 - Fairfax County, Virginia, Noise Ordinance applicability chart, maximum continuous sound levels in dBA Rule or law
“Residential Areas (as defined herein) in Residential Districts 10 p.m. to 7a.m., 55”
Quote checked on the page, 25 Oct 2026 - Fairfax County, Virginia, Noise Study Requirements, Data Centers Zoning Ordinance Amendment, Fall 2024 Rule or law
“The study must address the expected maximum noise output with all cooling and any other noise-generating equipment operating simultaneously at full operational load.”
Quote checked on the page, 25 Oct 2026 - Fairfax County, Virginia, Noise Study Requirements, Data Centers Zoning Ordinance Amendment, Fall 2024 Rule or law
“The Noise Ordinance also includes an exception for the routine testing and maintenance of back-up generators if the testing: a) occurs between 7 a.m. and 9 p.m.; and b) does not occur for more than two consecutive or nonconsecutive hours in any one day.”
Quote checked on the page, 25 Oct 2026 - City of Chandler, Arizona, Ordinance No. 5033 (data centers), adopted December 2022 Rule or law
“The Data Center must be designed and built to incorporate sound mitigation methods sufficient to prevent the sound levels emanating from the Data Center (as determined by a third-party acoustic engineer) from exceeding the ambient noise levels that were observed in the baseline study.”
Quote checked on the page, 25 Oct 2026 - City of Chandler, Arizona, Ordinance No. 5033 (data centers), adopted December 2022 Rule or law
“Unless the generators are supplying backup electrical supply during a power outage, backup generators may operate between the hours of 9:00 am and 5:00 pm, Monday through Friday, excluding holidays.”
Quote checked on the page, 25 Oct 2026
Cite this
Prince William Times (Piedmont Journalism Foundation), 27 February 2023 (archived copy), as quoted in Hum, “Why do people near data centres hear a constant hum, and how loud can it be?”, https://humearth.org/q/data-centre-noise (quote checked 25 Oct 2026).
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Why data centres hum: their cooling runs night and day. Fairfax County, Virginia, caps steady noise in residential areas at 55 dBA at night; Chandler, Arizona, says new ones can’t be louder than the background.